This invention relates to an improved process for making tris(hydroxyphenyl) compounds using ion exchange resins. More particularly, this invention relates to the preparation of 1, 1, 1-tris(4'-hydroxyphenyl)ethane that is substantially free of various impurities from phenol and 4-hydroxyacetophenone.
The condensation of phenol and 4-hydroxyacetophenone into 1, 1, 1-tris(4'-hydroxyphenyl)ethane (hereafter referred to as THPE) has generally been accomplished using mineral acids as catalysts. Examples of these reaction can be found in U.S. Pat. Nos. 3,579,542 (Meyer et al), 3,692,914 (Meyer et al), and 4,992,598 (Strutz, et al.). These preparation conditions typically require extended reaction times and lead to substantial amounts of various side products and relatively low yields of THPE.
THPE, having the general chemical structure as shown in Formula (I): ##STR1## is used as a hardener for epoxy resins and as a branching agent in thermoplastic resins, such as polycarbonate and polyester resins. As such, it is important that the material be pure and free of various possible isomers and impurities in order to fully obtain the desired properties in the final product. Recrystallization techniques have been developed for purifying THPE but are not quantitative for material recovery from the reaction mixture. An example of a crystallization technique for THPE can be found in U.S. Pat. No. 4,992,598 (Strutz, et al).
Other condensation reactions, for example, the conversion of various phenols and ketones into bis-phenols, have been accomplished with mineral acids or ion exchange resins as catalysts. In these condensation reactions for the production of bis-phenols using acids or ion exchange resins, elimination of the water by-product from the reaction mixture is not critical and conversions in excess of 90% to the desired bis-phenol are typical without removal of the water of reaction. Such reactions for the preparation of bis-phenols can be found in U.S. Pat. Nos. 3,049,568, 3,049,569 and 3,153,001 (Apel, et al) and 3,221,061 (Grover), among other references. During the condensation reactions for the production of bis-phenols using ion exchange resins, significant amounts of isomeric impurities, in addition to other unidentified impurities, are formed. As a result of the formation of undesirable contaminants, extensive efforts also have to be taken to purify the desired reaction product from the reaction mixture before it can be used in various polymerization reactions. The use of ion exchange catalysts for the preparation of tris-(hydroxyphenyl) compounds, for example THPE, is unknown.
Due to the costs and efforts associated with the conversion and subsequent purification of tris-(hydroxyphenyl) compounds and in particular THPE prepared using mineral acids to catalyze the condensation reactions, it is apparent that a need exists for improved methods for the preparation of these materials.